JP5573391B2 - Exhaust gas purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification system that collects PM (Particulate Matter) in exhaust gas of a diesel engine.

  Exhaust gas that collects PM in exhaust gas of diesel engine with DPF (Diesel Particulate Filter), for example, a filter called DPD (Diesel Particulate Defuser), which is a kind of exhaust gas, and reduces the amount of PM discharged to the outside A purification system has been developed (for example, Patent Document 1).

  As this exhaust gas purification system, there is a continuous regeneration type DPF system in which a DOC (Diesel Oxidation Catalyst) is provided on the upstream side of the DPF.

  The PM collected from the exhaust gas and deposited on the DPF causes clogging of the DPF and reduces the exhaust gas purification efficiency. Therefore, when a certain amount or more of PM is deposited on the DPF, the exhaust gas (for example, DPF regeneration is performed in which the temperature is raised to about 500 to 600 ° C., and PM is combusted (oxidized) and forcibly removed.

  The accumulated amount of PM is estimated from the output value of the differential pressure sensor that measures the differential pressure of the exhaust gas before and after the DPF. When the output value of the differential pressure sensor exceeds a predetermined differential pressure, the ECU (Engine Control Unit) Assuming that the amount of accumulated PM exceeds a predetermined amount, the ECU automatically starts DPF regeneration while the vehicle is running (automatic regeneration), or the driver who stops the vehicle after lighting the DPF warning lamp 35a performs regeneration Press the switch to start DPF regeneration (manual regeneration).

  In addition to the differential pressure of the exhaust gas before and after the DPF, the PM accumulation amount may be detected based on the travel distance. In this case, when the travel distance exceeds a predetermined distance, DPF regeneration is started automatically or manually as described above.

  When DPF regeneration starts, the fuel injector of the diesel engine is controlled, the exhaust gas temperature of the engine out is increased by multi-injection, and after the DOC is sufficiently warmed, unburned fuel is added to the exhaust gas. Then, by burning the fuel component in the DOC, the temperature of the exhaust gas flowing out from the DOC is raised to the regeneration target temperature (for example, about 500 to 600 ° C.), thereby forcibly burning the PM collected by the DPF. Remove.

  At this time, feedback control of the exhaust gas temperature is performed using the signal of the temperature sensor provided in the DPF, and the amount of unburned fuel added to keep the exhaust gas heated to the regeneration target temperature is PID. It is always adjusted by control.

  As a means for adding the unburned fuel described above, after the explosion stroke, the fuel is injected again from the fuel injector into the cylinder, and the unburned fuel is added to the exhaust gas remaining in the cylinder, and between the engine and the DPF. The exhaust pipe injector provided in the exhaust pipe is divided into exhaust pipe injection for adding unburned fuel to the exhaust gas exhausted from the engine and flowing through the exhaust pipe.

  Post-injection can use conventional diesel engines and exhaust gas purification systems as they are, but since unburned fuel is injected directly into the cylinder, fuel components are mixed into the engine oil and diluted to provide a lubricating function. Decreasing the oil causes problems of oil dilution such as cylinder burning.

  On the other hand, in DPF regeneration by exhaust pipe injection, there is no concern about the oil dilution described above, and DPF regeneration can be performed according to the amount of PM collected by the DPF.

Japanese Patent No. 4175281

  In the exhaust gas purification system using exhaust pipe injection, there is no concern about oil dilution during DPF regeneration as described above, so an upper limit is not set for the total amount of exhaust pipe injection until DPF regeneration is completed. Exhaust pipe injection can be performed.

  However, if the situation in which the temperature of the exhaust gas becomes insufficient during automatic regeneration (for example, a traffic jam in which start and stop are repeatedly performed) continues, temperature control becomes unstable and the exhaust gas rises sufficiently. There is a possibility that the temperature of the exhaust gas hardly reaches the temperature required for PM combustion without being heated, and in this case, the total amount of exhaust pipe injection used for the temperature rise control is abnormal before the DPF regeneration is completed. May increase.

  Even when various devices used for DPF regeneration (exhaust pipes, DOC that burns unburned fuel and raises the temperature of exhaust gas) are defective, it is difficult to raise the temperature of the exhaust gas. Exhaust pipe injection is performed indefinitely in order to perform regeneration, and fuel consumption may deteriorate.

  Accordingly, an object of the present invention is to accurately stop DPF regeneration and suppress deterioration of fuel consumption in a vehicle state where exhaust gas temperature rise control becomes unstable when performing DPF regeneration using exhaust pipe injection. It is to provide an exhaust gas purification system that can be used.

  The present invention was devised to achieve the above object, and is provided in an exhaust pipe of a diesel engine, and is provided in a DPF that collects PM in exhaust gas and the exhaust pipe upstream of the DPF. The exhaust pipe injector for exhaust pipe injection into the exhaust pipe, and when the PM collected by the DPF exceeds a certain amount, the exhaust gas temperature is raised by the exhaust pipe injection to regenerate the DPF. And a DPF regeneration control unit that accumulates the time during which the exhaust gas temperature exceeds the PM combustion temperature during the regeneration, and completes regeneration when the accumulated value reaches the regeneration completion set value. In the purification system, the DPF regeneration control unit determines an injection amount of exhaust pipe injection that becomes a predetermined temperature higher than the PM combustion temperature during regeneration, and the total amount of exhaust pipe injection during the regeneration is determined. When exceeding the trachea injection upper limit amount, an exhaust gas purification system, characterized in that stops the reproduction.

  According to the exhaust gas purification system of the present invention, when performing DPF regeneration using exhaust pipe injection, in a vehicle state in which the temperature rise control of exhaust gas becomes unstable, DPF regeneration is accurately stopped to improve fuel efficiency. Deterioration can be suppressed.

It is a system diagram showing a configuration of an exhaust gas purification system. It is a figure explaining operation | movement of an exhaust-gas purification system.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system diagram showing an exhaust gas purification system according to the present embodiment.

  In FIG. 1, an intake manifold 11 and an exhaust manifold 12 of a diesel engine 10 are respectively connected to a compressor 14 and a turbine 15 of a supercharger (turbocharger) 13, and air from the upstream intake pipe 16 a is boosted by the compressor 14. Then, the air is cooled through the intercooler 17 of the downstream side intake pipe 16b and supplied to the diesel engine 10 from the intake manifold 11 via the intake throttle (intake throttle valve) 18, and the exhaust gas from the diesel engine 10 passes through the turbine 15. After driving, the exhaust pipe 20 is exhausted.

The upstream intake pipe 16a is provided with a MAF (Mass Air Flow) sensor 19 for measuring the intake air amount. The MAF sensor 19 controls the opening of the intake throttle 18 to adjust the intake air amount. Also, the intake manifold 11 exhaust manifold 12 is connected to the EGR pipe 21 for reducing NO _X returns a part of exhaust gas to the intake system of the diesel engine 10, the EGR cooler 22 to the EGR pipe 21 EGR The valve 23 is connected.

  An exhaust brake valve 24, a DPF 25, an exhaust throttle (exhaust throttle valve) 26, and a silencer 27 are connected to the exhaust pipe 20. The DPF 25 includes a DOC 28 made of an active catalyst that oxidizes unburned fuel and a CSF (Catalyzed Soot Filter) 29 that collects PM in the exhaust gas.

  An exhaust pipe injector 38 for injecting fuel into the exhaust pipe 20 (exhaust pipe injection) is provided on the upstream side of the exhaust brake valve 24 in order to raise the exhaust gas temperature during DPF regeneration. A fuel supply line 39 for supplying fuel from a fuel tank (not shown) to the exhaust pipe injector 38 is connected to a fuel filter 40 for removing foreign substances and moisture mixed and generated in the fuel, and the exhaust pipe injector is disposed downstream thereof. A fuel pressure sensor 41 for measuring the fuel pressure 38 is provided.

Although not shown in FIG. 1, an SCR device is connected between the exhaust throttle 26 and the silencer 27. The SCR device is a device for purifying NO _{x in} exhaust gas by reacting with NH ₃ to form N ₂ and H ₂ O.

  Before and after the DOC 28, exhaust gas temperature sensors 30a and 30b used for determining whether exhaust pipe injection is possible, the exhaust pipe injection amount, and completion of DPF regeneration are provided. Further, in order to estimate the PM accumulation amount of the CSF 29, a differential pressure sensor 31 that measures the differential pressure of exhaust before and after the CSF 29 is provided.

  The output values of these sensors are input to an ECU 32 that performs overall control of the operation of the diesel engine 10 and also performs DPF regeneration, and the control signal output from the ECU 32 causes the fuel injector 33 of the diesel engine 10 and the exhaust gas to be exhausted. The throttle 26, the exhaust brake valve 24, the EGR valve 23, the exhaust pipe injector 38, and the like are controlled.

  In order to operate the diesel engine 10, the ECU 32 includes information such as the accelerator opening from the accelerator position sensor, the engine speed from the rotation speed sensor, the vehicle speed from the vehicle speed sensor 34, the temperature of the engine cooling water, and the like. Information is also entered.

  The ECU 32 also includes a DPF warning light 35a for manual regeneration provided in the cabin, a DPF warning light 35b for automatic regeneration, a regeneration execution switch 36 for the driver to perform manual regeneration, and a diesel engine 10. A check engine lamp 37 that is lit to notify the user when a problem occurs is connected and controlled.

  In this system, the air passes through the MAF sensor 19 in the upstream side intake pipe 16a, is pressurized by the compressor 14 of the supercharger 13, is cooled through the intercooler 17 in the downstream side intake pipe 16b, and is taken in the intake throttle 18 And enters the cylinder of the diesel engine 10 from the intake manifold 11.

  On the other hand, the exhaust gas generated in the cylinder passes through the exhaust manifold 12, drives the turbine 15, is purified by the exhaust gas purification system including the DPF 25 and the SCR device, is silenced by the silencer 27, and is discharged into the atmosphere. A part of the exhaust gas is cooled by the EGR cooler 22, the amount thereof is adjusted by the EGR valve 23, and circulated to the intake manifold 11.

The exhaust gas contains PM, and this PM is collected by the DPF 25. In the DPF 25, NO in the exhaust gas is oxidized to NO ₂ by the DOC 28 at all times, and the PM collected in the downstream CSF 29 is oxidized to CO ₂ with this NO ₂ to remove the PM from the CSF 29. In other words, so-called DPF regeneration is continuously performed.

  However, when the exhaust gas temperature is low, the temperature of the DOC 28 is lowered and is not activated, so that the oxidation reaction is not promoted and PM cannot be oxidized and DPF regeneration cannot be performed. Will continue and the clogging of the filter will proceed.

  For this filter clogging, the exhaust gas temperature is forcibly raised when the PM accumulation amount exceeds a predetermined accumulation amount, and the PM collected in the CSF 29 is forcibly burned and removed. Is done.

  Since the PM accumulation amount is proportional to the output value of the differential pressure sensor 31, when the output value of the differential pressure sensor 31 exceeds a predetermined differential pressure (differential pressure threshold), the ECU 32 detects clogging of the filter, The ECU 32 automatically performs DPF regeneration or turns on the DPF warning lamp 35a and prompts the driver to press the regeneration execution switch 36 to perform DPF regeneration. In this way, the DPF regeneration for determining the start timing based on the differential pressure is the differential pressure regeneration. Hereinafter, DPF regeneration automatically performed by the ECU 32 is referred to as automatic regeneration, and regeneration performed manually by the driver is referred to as manual regeneration.

  In addition to the output value of the differential pressure sensor 31, the start time of DPF regeneration is determined by whether or not the travel distance calculated based on the vehicle speed measured by the vehicle speed sensor 34 exceeds a predetermined distance (distance threshold). You may do it. Thus, DPF regeneration that determines the start time based on the travel distance is distance regeneration.

  An example of manual regeneration and automatic regeneration will be described.

  Manual regeneration is performed with the vehicle stopped. When the user depresses the regeneration execution switch 36 and the manual regeneration is started after the vehicle is stopped, the ECU 32 controls the fuel injector 33, the diesel engine 10, the exhaust brake valve 24, the EGR valve 23, and the intake throttle 18, and the exhaust The gas temperature is raised to a temperature at which the DOC 28 is activated.

  More specifically, the ECU 32 controls the fuel injector 33 to start multi-injection, controls the diesel engine 10 to increase the engine speed, closes the exhaust brake valve 24 for rapid temperature rise, and sets the EGR valve. 23 is closed to prevent recirculation of the fuel, and the intake throttle 18 is controlled to reduce the intake amount, thereby suppressing the temperature drop and increasing the load.

  The activation of the DOC 28 is determined based on whether the detected value of the exhaust gas temperature sensor 30a upstream of the DOC 28 is equal to or higher than a preset upstream threshold value, and the detected value of the exhaust gas temperature sensor 30b downstream of the DOC 28 is previously determined. This is done when the set downstream threshold is exceeded. That is, the activation of the DOC 28 is determined from the detection values of both the upstream and downstream exhaust gas temperature sensors 30a, 30b of the DOC 28.

  When the DOC 28 is activated, the exhaust pipe injector 38 is controlled together with the multi-injection to start the exhaust pipe injection, the exhaust brake valve 24 is opened, the exhaust throttle 26 is closed, and the exhaust gas temperature is further raised to the target temperature.

  At this time, the target temperature is set, for example, in two stages of a regeneration target temperature (initial) and a regeneration target temperature (late) higher than the regeneration target temperature (initial), and each target temperature is maintained for a predetermined time. The ECU 32 is controlled. The reason why the target temperature is set in multiple stages is to prevent the CSF 29 from being melted by heat generated by burning PM. That is, in the initial stage of DPF regeneration in which a large amount of PM remains, a large amount of heat is generated due to the combustion of PM. Is set high so that PM burns efficiently.

  Thereafter, the ECU 32 controls the fuel injector 33 to return to normal injection, closes the exhaust pipe injector 38, controls the diesel engine 10 to return the engine speed to the normal idle state, opens the exhaust throttle 26, The EGR valve 23 is returned to normal (open), and the intake throttle 18 is returned to normal (open). Thereby, exhaust gas temperature falls and manual regeneration is complete | finished.

  In this manual regeneration, since the DPF regeneration is performed with the vehicle stopped, the exhaust gas temperature can be kept stable and PM can be burned efficiently and reliably, while the vehicle is stopped during the manual regeneration. Therefore, it is necessary to wait for a predetermined time.

  Next, automatic reproduction will be described.

  Automatic regeneration is performed while the vehicle is running. When the automatic regeneration is started by the ECU 32, the ECU 32 controls the fuel injector 33, the diesel engine 10, the EGR valve 23, and the intake throttle 18, and raises the exhaust gas temperature to a temperature at which the DOC 28 is activated. In the automatic regeneration, the exhaust brake valve 24 cannot be closed because the vehicle is running unlike the manual regeneration. However, when the vehicle is stopped, such as waiting for a signal, the exhaust brake valve 24 is closed to increase the exhaust pressure and the exhaust gas temperature. Keep warm.

  When the DOC 28 is activated (the determination criteria for the activation of the DOC 28 are the same as described above), the exhaust pipe injector 38 is controlled together with the multi-injection to start the exhaust pipe injection, and the exhaust gas temperature is further raised to the target temperature. Since the exhaust throttle 26 cannot be closed because the vehicle is running, the exhaust throttle 26 is always open.

  Thereafter, when the exhaust gas temperature rises to the target temperature and is maintained for a predetermined time, the ECU 32 controls the fuel injector 33 to return to normal injection, closes the exhaust pipe injector 38, controls the diesel engine 10 and controls the engine speed. Is returned to normal, the EGR valve 23 is returned to normal (open), and the intake throttle 18 is returned to normal (open). Thereby, exhaust gas temperature falls and automatic regeneration is complete | finished.

  In this automatic regeneration, since the DPF regeneration is performed while the vehicle is running, it is more convenient than the manual regeneration. On the other hand, in the automatic regeneration, the exhaust gas temperature is not stabilized or does not rise easily, and the exhaust pipe injection amount is increased compared with the manual regeneration, and the fuel consumption tends to deteriorate.

  Thus, automatic regeneration and manual regeneration each have advantages and disadvantages, and it can be said that it is preferable to select and use them appropriately according to the situation.

  Selection of automatic regeneration or manual regeneration is made based on a regeneration interval that is a travel distance from the end of DPF regeneration to the start of the next DPF regeneration. Specifically, when the regeneration interval is less than the set manual regeneration threshold, the driver is prompted to perform manual regeneration.

  The reason why PM accumulates in the DPF exceeding the threshold value even though the regeneration interval is short, that is, the traveling distance is short, may be that PM was not sufficiently removed by the previous DPF regeneration. Therefore, when the regeneration interval is less than the manual regeneration threshold, manual regeneration that can stably perform DPF regeneration is selected to reliably remove PM.

  By the way, if the situation in which the temperature of the exhaust gas becomes insufficient during automatic regeneration (for example, a traffic jam in which start and stop are repeatedly performed) continues, the temperature of the exhaust gas becomes insufficient and the exhaust gas Since the temperature does not reach the combustion temperature of PM, the PM is hardly burned and removed, and the exhaust pipe injection used for the temperature rise control is completed until the exhaust gas temperature is maintained at the regeneration target temperature for a certain period of time and the DPF regeneration is completed. The total amount may increase without limit.

  Further, even when various devices (such as DOC28) used for DPF regeneration are defective and it is difficult to raise the temperature of the exhaust gas, the ECU 32 may perform exhaust pipe injection indefinitely to perform DPF regeneration. There is.

  Therefore, in the exhaust gas purification system of the present invention, the ECU 32 includes the DPF regeneration control unit 100, and the DPF regeneration control unit 100 further includes an incomplete regeneration warning unit 101 and an abnormality warning unit 102.

  During regeneration, the DPF regeneration control unit 100 accumulates the time during which the exhaust gas temperature exceeds the PM combustion temperature (hereinafter referred to as regeneration time), and when the integrated value reaches the regeneration completion set value, regeneration is performed. When the total amount of exhaust pipe injection exceeds the exhaust pipe injection upper limit value before the regeneration is completed, the regeneration is stopped because the regeneration has failed.

  Further, the DPF regeneration control unit 100 operates the regeneration incomplete warning means 101 to warn the driver that the regeneration has failed when the total amount of exhaust pipe injection exceeds the exhaust pipe injection upper limit value. .

  Further, the DPF regeneration control unit 100 determines that an abnormality has occurred in the exhaust gas purification device or device when the regeneration failure has continued for a predetermined number of times, that is, a malfunction has occurred in the exhaust pipe 20 itself, the DOC 28, or the like. The abnormality warning means 102 for warning the abnormality is activated.

  The present invention does not particularly limit the regeneration incomplete warning means 101 and the abnormality warning means 102. For example, the DPF warning lights 35a and 35b are blinked as the regeneration incomplete warning means 101, and the check engine lamp is used as the abnormality warning means 102. 37 may be turned on, and can be appropriately changed using various warning means provided in the vehicle.

  The operation of the present invention will be described below.

  FIG. 2 explains the operation of the exhaust gas purification system according to the present embodiment and the transition of the exhaust gas temperature, particularly in automatic regeneration.

  When it is detected that the amount of PM collected in the DPF 25 has become a certain amount or more, the DPF regeneration control unit 100 mounted on the ECU 32 starts the exhaust gas temperature raising control to regenerate the DPF 25.

  The DPF regeneration control unit 100 controls the fuel injector 33 to perform multi-injection, increases the exhaust gas temperature of the engine out, and the temperature of the exhaust gas flowing into the DOC 28 by the temperature sensors 30a and 30b provided before and after the DOC 28. Is detected to reach the catalyst activation temperature of the DOC 28, the exhaust pipe injector 38 is controlled to perform the exhaust pipe injection and the exhaust pipe injection amount is integrated in order to further raise the exhaust gas temperature to the regeneration target temperature. Start.

  At this time, the DPF regeneration control unit 100 performs feedback control using a deviation between the exhaust gas temperature detected by the temperature sensor 30b and the regeneration target temperature, and the exhaust pipe injection amount necessary for maintaining the exhaust gas at the regeneration target temperature. Are adjusted by PID control.

  When the DPF regeneration control unit 100 detects that the exhaust gas temperature is equal to or higher than the PM combustion temperature lower than the regeneration target temperature by a predetermined temperature (A ° C.), the DPF regeneration control unit 100 determines that the PM is combusting and determines the regeneration time. Accumulated.

  As the PM combustion temperature, a minimum temperature that can guarantee that PM is burning is obtained from a simulation test or the like, and DPF regeneration may be performed with this as a fixed value. Depending on the amount of collected PM, the DPF regeneration control unit 100 may be able to change the PM combustion temperature as appropriate.

  During regeneration, when the regeneration time to be accumulated reaches a predetermined value (B minutes), the DPF regeneration control unit 100 assumes that the PM collected in the DPF 25 has been burned and removed to a certain amount or less, and the exhaust gas rises. The temperature target temperature (that is, the regeneration target temperature) is changed to the high temperature side.

  In the initial stage of DPF regeneration, DPF regeneration is performed at a relatively low temperature (for example, about 500 ° C.) in order to prevent overheating of the DPF 25 and melting damage due to the combustion heat of PM. In this case, PM can be efficiently burned and removed by changing the regeneration target temperature to the high temperature side (for example, about 600 ° C.).

  At this time, the PM combustion temperature may be changed according to the changed target temperature so as to be lower than the changed target temperature by a predetermined temperature (A ° C.). Alternatively, it may be set in advance so as to consist of two stages of fixed values.

  When exhaust gas temperature rise control is stably performed and the exhaust gas temperature is sufficiently maintained above the PM combustion temperature, the integrated value of the regeneration time is greater than a predetermined value (B minutes) obtained by changing the regeneration target temperature. When the regeneration completion set value (C minutes) that is set to be larger is reached, the DPF regeneration control unit 100 determines that regeneration of the DPF 25 has been completed, assuming that the PM collected in the DPF 25 has been sufficiently removed, Control is performed to return the vehicle to a normal driving state or an idle state.

  On the other hand, if the temperature control of the exhaust gas being regenerated is unstable and the temperature of the exhaust gas is hardly maintained above the PM combustion temperature, the total amount of exhaust pipe injection will be exhausted before the regeneration time reaches the regeneration completion set value. When the pipe injection upper limit is exceeded, the DPF regeneration control unit 100 determines that regeneration has failed and performs control to return the diesel engine 10 to a normal operation state or idle state, and warns the driver that regeneration has not been completed. The incomplete reproduction warning means 101 is activated.

  As a result, when the vehicle is not in a situation where the exhaust gas temperature can be sufficiently raised, by stopping the DPF regeneration and the exhaust pipe injection, the deterioration of fuel consumption can be suppressed, and the next DPF regeneration can be stabilized. Can be encouraged to do so.

  Further, when regeneration is not completed continuously, defects occur in various devices (for example, the exhaust pipe 20 itself, the DOC 28, etc.) that control the temperature rise of the exhaust gas, and it becomes difficult to raise the temperature of the exhaust gas. There is a strong possibility that.

  Therefore, the DPF regeneration control unit 100 of the exhaust gas purification system according to the present invention determines that an abnormality has occurred in the exhaust gas purification device or device when the regeneration failure continues for a predetermined number of times, By operating the abnormality warning means 102 for warning the abnormality, it is possible to notify the driver of the abnormality and prompt prompt inspection and repair.

  It goes without saying that the present invention is not limited to the above embodiment and can be appropriately changed without departing from the gist of the present invention.

25 DPF
38 Exhaust pipe injector 100 DPF regeneration control unit

Claims (1)

A DPF which is provided in an exhaust pipe of a diesel engine and collects PM in exhaust gas; an exhaust pipe injector which is provided in the exhaust pipe upstream of the DPF and which performs exhaust pipe injection in the exhaust pipe; When the PM collected by the DPF exceeds a certain amount, the exhaust gas temperature is raised by the exhaust pipe injection to regenerate the DPF, and the exhaust gas temperature exceeds the PM combustion temperature during the regeneration. In an exhaust gas purification system comprising a DPF regeneration control unit that accumulates time and completes regeneration when the integrated value reaches a regeneration completion set value,
The DPF regeneration control unit determines an injection amount of exhaust pipe injection that becomes a predetermined temperature higher than the PM combustion temperature during regeneration, and the total amount of exhaust pipe injection exceeds an exhaust pipe injection upper limit value during the regeneration An exhaust gas purification system characterized by stopping regeneration.

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